The present invention relates generally to plural component dispensing devices, and more specifically to a spray gun for applying chemically reactive plural components while maintaining fluid isolation between the components to the point where they are introduced into a common mixing chamber for spraying.
The field relating to the spraying and dispensing of chemically reactive liquid components presents particularly difficult design problems for the dispensing nozzle, because the respective components must be maintained in complete fluid isolation up to the moment of spraying or dispensing. Typically, plural components of the type relating to the present invention comprise a resin component which is chemically inert in isolated form and an isocyanate material which is also chemically inert in isolated form. When the isocyanate and resin are combined an immediate chemical reaction begins taking place and, depending upon the selection of materials, typically results in a relatively fast solidifying process of the mixed materials. Industrial foams for packaging, insulation, and other uses are usually formed in this manner, and upon hardening they become solid materials. If the hardening process occurs within the spray gun or dispenser the various passages and ports will become clogged and blocked by the materials and the spraying or dispensing device will be totally disabled. Further, the task of cleaning such materials from internal passages and ports of a spraying device is extremely difficult, and in many cases the device must be completely rebuilt or replaced.
Prior art devices have addressed the problem of mixing and dispensing chemically reactive components with varying degrees of success. U.S. Pat. No. 2,890,836, issued June 16, 1959 discloses a mixing chamber placed proximate a spray orifice, having a slidable plunger therein for completely closing the mixing chamber and spray orifice in a first position and for opening diametrically displaced jets into the mixing chamber in a rearward position. Because of the extremely short distance between the mixing chamber and the spray orifice, this device is susceptible of imperfect mixing. U.S. Pat. No. 3,144,210, issued Aug. 11, 1964, discloses a mixing chamber having axially displaced inlet ports, one set of ports comprising a plurality of passages tangentially aligned to the mixing chamber and normal to the axis of the mixing chamber; the second set of inlet ports comprising tangentially aligned ports with respect to the mixing chamber, but angled in a forward direction with respect to the spray nozzle. U.S. Pat. No. 3,263,928, issued Aug. 2, 1966, discloses a mixing chamber having axially aligned but diametrically displaced ports, wherein the mixing chamber is formed of two identical half-circle parts, and wherein packing sleeves are axially compressed on either side of the mixing chamber. U.S. Pat. No. 3,799,403, issued Mar. 26, 1974, discloses a movable mixing chamber which is positionable to accept a purging gas upon termination of the dispensing operation. U.S. Pat. No. Re. 29,665, reissued June 13, 1978 discloses a mixing chamber having axially displaced inlet ports, and having a narrowed throat axially intermediate the inlet ports, and having a movable plunger arranged for interference fit with the throat. U.S. Pat. No. 4,133,483, issued Jan. 9, 1979, discloses an independently actuable purging rod slidably displaced in the mixing chamber, which may be retracted for admitting solvent or air purging materials.
The foregoing patents suffer from problems relating to imperfect fluid isolation seals, inadequate mixing chambers, and unreliable purging of the mixed components at the termination of the spraying operation, unless solvent or other purging gases are utilized for cleaning. Further, in many cases the sealing problems require complex constructions of seals in combination with the mixing chamber in order to attempt to obtain an adequate solution. There is a need for a mixing chamber construction which is both simple and efficient, and which requires a minimum number of complex parts for construction.
It is the principal object of the present invention to provide a spray gun nozzle having a simple and effective mixing chamber, with positive fluid seals for maintaining liquid isolation of the respective components. It is another object of the invention to provide a spray gun nozzle for a plural component dispensing device which is simple to disassemble for cleaning.
It is further object of the present invention to provide a one piece spray gun mixing chamber having precisely positioned inlet orifices for passage of at least two liquid components, and having thereon liquid sealing members to provide isolation between the components.